When gonadotropin-releasing hormone (GnRH) agonist and antagonist peptide medications were first approved for use in the 1980s and 1990s, the available agents could only be administered by injection or nasal spray. The innovative development of orally active, nonpeptide GnRH antagonists, including relugolix and elagolix (FIGURE 1), is a major breakthrough in women’s health. Orally active GnRH antagonists provide gynecologists with a unique way to regulate hypothalamic-pituitary-ovarian-uterus function. GnRH antagonists bind to the pituitary GnRH receptor, reducing pituitary secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). In turn, reduction in LH and FSH suppresses ovarian follicle development, reducing ovarian secretion of estradiol and progesterone. The uterine endometrium becomes less active in response to low levels of estradiol and progesterone, resulting in oligomenorrhea or amenorrhea. The hypoestrogenic adverse effects of GnRH antagonist treatment, including bone loss and vasomotor symptoms can be minimized by adding back a low dose of estrogen and progestin, such as oral estradiol 1 mg and norethindrone acetate 0.5 mg.
Recently, the US Food and Drug Administration (FDA) approved oral relugolix combination therapy (Myfembree, Myovant Sciences and Pfizer Inc; relugolix 40 mg, estradiol 1 mg, and norethindrone acetate 0.5 mg) once daily for the treatment of abnormal uterine bleeding (AUB) associated with uterine leiomyomata (fibroids) in premenopausal women for up to 24 months.1 This editorial will focus on key clinical issues when using relugolix combination therapy.
Relugolix combination treatment is superior to placebo for AUB from fibroids
In 2 clinical trials, 770 women with symptomatic uterine fibroids were randomly assigned to 1 of 3 groups2:
- placebo for 24 weeks
- relugolix combination therapy (consisting of relugolix 40 mg, estradiol 1 mg, and norethindrone acetate 0.5 mg) daily for 24 weeks
- relugolix monotherapy (40 mg daily for 12 weeks) followed by relugolix combination therapy for 12 additional weeks (delayed combination therapy group).
The women’s mean age was approximately 42 years, and they had a mean menstrual blood loss at baseline of approximately 230 mL and mean uterine volume by ultrasound measurement of 408 cm3.2 Prior to entry into the study all the women had an endometrial biopsy and a transvaginal ultrasound study of the pelvis. Women with a baseline bone mineral density Z-score of less than -2.0 at the spine, total hip, or femoral neck were excluded from the study because of low bone mass.2
At 24 weeks of treatment, approximately 72% of the women in the relugolix combination therapy groups had less than 80 mL of menstrual blood volume loss and ≥50% reduction in menstrual blood loss from baseline compared with 17% of women in the placebo group.2 At 8 weeks of treatment mean percent changes in menstrual blood loss from baseline were approximately 80% and 20% for the women receiving relugolix combination and placebo, respectively. Those differences persisted from 8 weeks through 24 weeks of treatment.1 In the last 35 days of treatment, amenorrhea was reported by approximately 51% and 4.5% of women receiving relugolix combination or placebo treatment, respectively.2 Compared with the placebo group, the relugolix combination groups reported significant improvement in bleeding and pelvic discomfort and had a higher hemoglobin concentration. Compared with placebo, relugolix combination treatment resulted in a greater percentage decrease in uterine volume (-12.9% vs +2.2%, respectively; P< .001).2
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